JP2003207635A - Object identification medium and identification method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an identification medium and identification for an object which cannot be easily forged, and which can be provided with characters and designs freely, and which can be easily manufactured and provided at low cost. Provide a method. SOLUTION: Out of the vertically incident light, only specific circularly polarized light of a specific color is reflected by liquid crystal particles 12, and other components are transmitted through the liquid crystal particles and absorbed by the object 1. When the object 1 is viewed from the front, specific points appear to be dispersed, and when the viewing angle is increased, the short wavelength points appear to be dispersed. When the viewing angle is further increased, the short wavelength points are dispersed. appear.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to authenticity of flat objects such as passports, cards, banknotes, cash vouchers, securities, certificates, gift certificates, paintings, tickets, public competition voting tickets, and various three-dimensional objects. The present invention relates to an identification medium and an identification method for identifying sex.

[0002]

2. Description of the Related Art Conventionally, as a method for preventing forgery of a card or a certificate, for example, a technique of attaching a hologram or applying a special ink on the surface of the object is known. In the hologram, it was identified by visually confirming that it looks three-dimensional and that the color changes depending on the viewing angle. In addition, there are fluorescent inks and magnetic inks as special inks, which are no different from normal inks by visual inspection, but by irradiating ultraviolet rays or detecting with a magnetic sensor, the target information is identified by hidden information. be able to.

[0003]

However, as the hologram manufacturing technology has become widespread, the counterfeit technology has improved, and it has become possible to easily manufacture a counterfeit product that is indistinguishable from a genuine product. Further, the fluorescent ink and the magnetic ink have similar drawbacks that they are easy to forge because similar products are easily available, and the device for identification is large and requires a power source, which is not convenient.

In Japanese Unexamined Patent Publication No. 4-144796, random light is irradiated to a cholesteric liquid crystal, the reflected circularly polarized light is converted into linearly polarized light by a quarter-wave plate through a bandpass filter, and this linearly polarized light is converted into a beam. Split with a splitter,
A technique for detecting right or left circularly polarized light by a polarizing plate in each direction is disclosed. In this technique, since the cholesteric liquid crystal is a uniform sheet over the entire surface, it is not easy to freely add characters and patterns, and there are drawbacks in that there are large design restrictions.

Australian Patent No. 488652
The publication discloses a technique of dispersing a cholesteric liquid crystal in ink and printing it on an object. However, in this technique, since the liquid cholesteric liquid crystal is filled in the microcapsules, the manufacturing process is complicated, and the microcapsules are easily damaged, which is not practical.

Therefore, according to the present invention, it is not possible to easily forge, and at the same time, characters and patterns can be freely provided, and the identification medium and identification of the object which can be easily manufactured and provided at low cost. It is intended to provide a way.

[0007]

DISCLOSURE OF THE INVENTION The present invention is an object identification medium for identifying the authenticity of an object by optically providing an object with an identification display such as a character or a pattern. ,
It is characterized in that the identification mark is formed by particles of a film having a light-reflecting layer of a polymer cholesteric liquid crystal having a circularly polarized light selectivity for reflecting a specific circularly polarized light.

First, the basic principle of the present invention will be described. FIG. 1 is a diagram showing the structure of a cholesteric liquid crystal. The cholesteric liquid crystal has a layered structure, and the molecular major axis directions in each layer are parallel to each other and parallel to the layer surface. In addition, each layer rotates slightly and overlaps,
It has a three-dimensional spiral structure. This direction factor is 360
The distance to rotate back to the original position, that is, the pitch P,
From the average refractive index n in each layer, it has a characteristic of selectively reflecting circularly polarized light having a central wavelength λs represented by λs = n · P (circularly polarized light selectivity). Therefore, as shown in FIG. 2, if the direction of the cholesteric liquid crystal of each layer is clockwise with respect to the incident light, the right circularly polarized light of the component of the central wavelength λs is reflected as it is, and the left circularly polarized light is transmitted through the cholesteric liquid crystal. In addition, all light of other wavelengths passes through the cholesteric liquid crystal. For example, a cholesteric liquid crystal that reflects the central wavelength λs of red is placed on a material such as black paper that absorbs visible light, and when random light such as sunlight is applied, all transmitted light is absorbed by the black paper, Since only the right-handed circularly polarized light having the center wavelength λs is reflected by the cholesteric liquid crystal, the cholesteric liquid crystal looks bright red.

Further, the cholesteric liquid crystal is characterized in that its color changes depending on the viewing angle. This is because when the incident light is oblique, the pitch P apparently decreases and the center wavelength λs shifts to the short wavelength side. For example, the reflection color of cholesteric liquid crystal that turns red by observing vertically incident light is observed to change sequentially as the viewing angle increases to orange, yellow, green, turquoise, and blue (blue shift). ).

In the identification medium of the object of the present invention, the identification display is formed of particles of a film having a light-reflecting layer of a polymer cholesteric liquid crystal having a circular polarization selectivity for reflecting a specific circular polarization. Therefore, the individual particles have circular polarization selectivity and blue shift as described above. Therefore, the object provided with such an identification medium can be visually identified whether it is a genuine product or not by the colors observed from the vertical direction and the oblique direction.

In the present invention, by using the optical filter, the identification can be performed more surely. That is, by observing the identification display through the first filter that transmits only the circularly polarized light of the light reflecting layer and the second filter that transmits only the circularly polarized light in the opposite direction to the circularly polarized light of the light reflecting layer, Identify things. In this case, when the object provided with the identification medium of the present invention is viewed through the first filter, it looks like a predetermined color, and when the viewing angle is increased, blue shift occurs, but
I can't see anything through the filter. Further, only specific circularly polarized light (for example, right circularly polarized light) is transmitted through the first filter, and the circularly polarized light is reflected by the light reflecting layer and is transmitted through the first filter again, so that the light seen through the first filter is seen. Becomes clearer.

On the other hand, when the identification display is provided by simple printing of ink or the like, the light reflected by the identification display is random natural light, and therefore the circularly polarized light of the light reflection layer is included in the component of the light. Is transmitted through the first filter, and the circularly polarized light in the opposite direction is transmitted through the second filter, but the circularly polarized light includes light of all wavelengths, and the left and right circularly polarized light include almost the same amount. I'm out. Therefore, the same thing can be seen through the first and second filters. Further, when the identification display is formed by the particles of the polymer cholesteric liquid crystal having the circularly polarized light opposite to the authentic one, nothing is seen when the object provided with the identification medium is viewed through the first filter. Instead, it looks like a predetermined color when viewed through the second filter. Therefore, even in this case, it is possible to identify the product as a counterfeit product.

According to the present invention, since the identification display is formed by the particles of the film having the light-reflecting layer of the polymer cholesteric liquid crystal, the particles can be dispersed in ink or the like to print arbitrary characters or patterns. It is possible to cope with the diversification of design. Further, since the film having the light-reflecting layer of the polymer cholesteric liquid crystal can be crushed into particles, it is easy to manufacture. In addition, polymer cholesteric liquid crystal is used only for letters and patterns, and the mixing amount of polymer cholesteric liquid crystal particles can be freely changed, so material cost is reduced and manufacturing cost is greatly reduced. You can Further, the authenticity of the object can be visually and easily determined.

Although the identification medium of the present invention is simple to manufacture,
Forgery of the object provided with it is not easy. That is,
Particles of a film having a reflective layer of a polymer cholesteric liquid crystal contained in the identification medium of the present invention, and a coating material such as ink containing the particles are duplicated, and furthermore, the same printing must be applied to an object, Manufacturing counterfeit products is extremely difficult.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. 1. Polymer cholesteric liquid crystals Polymer cholesteric liquid crystals are disclosed in JP-A-63-51193.
JP-A-57-165480, JP-A-58
It can be produced by a known method disclosed in Japanese Patent Publication No. 17119. For example, a low-molecular cholesteric liquid crystal is dissolved and held in a polymerizable monomer to grow the cholesteric liquid crystal, and then the low-molecular liquid crystal is cross-linked by photoreaction or thermal reaction to fix the molecular orientation and polymerize it. To do. Alternatively, after heating the side chain type or main chain type thermotropic polymer liquid crystal above its liquid crystal transition point to grow a cholesteric liquid crystal structure, it is cooled to a temperature below the liquid crystal transition point to fix the molecular orientation. Is also good. Further, after the side chain type or main chain type lyotropic polymer liquid crystal is cholesterically aligned in a solvent, the solvent may be gradually volatilized to fix the molecular orientation.

Specifically, side chain type polymers such as polyacrylates, polymethacrylates, polysiloxanes and polymalonates having a liquid crystal forming group in the side chain, polyesters and polyesteramides having a liquid crystal forming group in the main chain,
Main chain type polymers such as polycarbonate, polyamide and polyimide can be mentioned.

The polymer cholesteric liquid crystal as described above can be produced by applying a raw material liquid to one surface of a thin plastic film having a release layer and fixing cholesteric orientation and molecular orientation. In this case, the polymer cholesteric liquid crystal has a uniform twist pitch P along the stacking direction of molecules and a thickness of about 0.5 to 5.0 μm.

2. Production of Liquid Crystal Particles The polymer cholesteric liquid crystal is peeled off from the sheet produced as described above and pulverized by a pulverizer. A rotary mill, a ball mill, or the like can be used as the crusher. The crushed polymer cholesteric liquid crystal particles (hereinafter, referred to as “liquid crystal particles”) are foils, and it is desirable that the surface thereof be arranged substantially parallel to the surface of the object. This unifies the colors of circularly polarized light reflected by each liquid crystal particle when viewed from one direction. Therefore, the size of the liquid crystal particles is preferably 10 μm or more.
If the size of the liquid crystal particles exceeds 500 μm, the unevenness of the printing surface becomes severe and the printing texture becomes rough.
When manufacturing the liquid crystal particles, the sheet can be crushed together. In this case, it is necessary to use a transparent sheet having a small birefringence. The thickness of the sheet is 5 to 2
0 μm is suitable. Further, the size of the liquid crystal particles including the sheet is preferably 50 to 500 μm for the same reason as above.

3. Coating Liquid crystal particles produced as described above are mixed with a vehicle. The ratio of liquid crystal particles to the vehicle is arbitrary,
0.1 to 10% by weight is suitable. Vehicles include oils such as vegetable oils, processed oils, mineral oils, natural resins, natural product derivatives,
Resins such as synthetic resins, hydrocarbons, alcohols, esters,
There are solvents such as ketones, glycols and their derivatives, which can be appropriately selected. The vehicle is preferably transparent, but may be lightly colored with a dye. Then, the coating liquid thus produced is printed on an object by screen printing, offset printing, or the like. As a result, the identification display in which the liquid crystal particles are uniformly dispersed is formed on the printed surface.

FIG. 3A is a sectional view showing the identification medium 10 provided on the black object 1 as described above. In the figure, reference numeral 11 is a vehicle, and 12 is a liquid crystal particle. In the liquid crystal particles 12, the pitch at which the molecular orientation spiral rotates 360 degrees is adjusted so as to reflect the vertically incident red right circularly polarized light. As a result, of the vertically incident light, only red right-handed circularly polarized light is reflected by the liquid crystal particles 12, and other components are transmitted through the liquid crystal particles and absorbed by the object 1. In addition, as shown in FIG.
Has a thickness t of 1 to 2 μm and a particle diameter D of about 100 μm. Since the liquid crystal particles 12 are foils having a small thickness with respect to the particle size, the liquid crystal particles 12 are substantially parallel to the object 1 when applied to the object 1. Therefore, when the object 1 is viewed from the front, the red dots appear dispersed, the green dots appear dispersed as the viewing angle is increased, and the blue dots are dispersed when the viewing angle is further increased. appear.

In the embodiment shown in FIG. 3, the liquid crystal particles 12 are substantially parallel to the object 1. However, the present invention is not limited to such a configuration, and the liquid crystal particles 12 are You may face in a random direction. However,
In this case, no matter which direction the identification medium 10 is viewed from,
Since the blue dots appear to be dispersed, it is undeniable that the effects of the blue shift are difficult to understand and counterfeiting is a little easier.

FIG. 4 is a diagram showing a method of identifying the object 1 using the circular polarization filter 2. Circular polarization filter 2
Is a first filter 2a which transmits only right circularly polarized light,
And a second filter 2b that transmits only left-handed circularly polarized light. These first and second filters 2a,
2b is a wave plate 21a, 21b and a polarizing plate 22a, 22
It consists of b. Here, the polarizing plates 22a and 22b are
Only light with a specific wave direction is transmitted to make it linearly polarized. Further, the wave plates 21a and 21b shift the phase of a part of the linearly polarized light by 1/4 of the wavelength to make the linearly polarized light into circularly polarized light. In this embodiment, light entering from the polarizing plate 22a side is linearly polarized by the first filter 2a and then becomes right circularly polarized light, and second light 2b becomes left circularly polarized light. The wave plates 21a and 21b convert the incident circularly polarized light into linearly polarized light or convert the linearly polarized light into circularly polarized light.

In the right-handed circularly polarized light emitted from the first filter 2a, only the component of the wavelength determined by the pitch is liquid crystal particles 12
Is reflected by and is incident on the first filter 2a again as right circularly polarized light. At that time, the right-hand circularly polarized light is emitted as linearly polarized light by the first filter 2a. Thus, since only the right-handed circularly polarized light is left by the first filter 2a, the image seen through the first filter 2a is
It is sharper than when viewed with the naked eye. On the other hand, the left-handed circularly polarized light emitted from the second filter 2b passes through the liquid crystal particles 12 and is absorbed by the object 1. Therefore, the second filter 2b only looks black and nothing. in this case,
Due to the second filter 2b, only the left-handed circularly polarized light is the liquid crystal particles 1.
The second filter 2b becomes darker than the case where it is visually recognized by the naked eye, and the contrast with the image seen through the first filter 2a becomes strong because the second filter 2b is incident on the second filter 2 and all of them are transmitted through the liquid crystal particles 12.

When the object 1 is viewed from the front using the circular polarization filter 2 as described above, a red image of the identification medium 10 can be seen through the first filter 2a, and blue shift occurs when the viewing angle is increased. Nothing can be seen through the second filter 2b. This allows the object 1 to be identified as authentic.

On the other hand, when the identification medium 10 is provided by simple printing of ink or the like, the light reflected by the identification medium 10 is random natural light, so that the right-handed circularly polarized light is a component of the light. The left circularly polarized light passes through the first filter 2a and the left circularly polarized light passes through the second filter 2b. However, the circularly polarized light includes light of all wavelengths, and the left and right circularly polarized light include substantially the same amount. There is. Therefore, the same thing can be seen through the first and second filters 2a and 2b. In addition, liquid crystal particles 12 having circularly polarized light in the opposite direction to the true one
If the identification medium 10 is formed of, the identification medium 1
When 0 is viewed through the first filter 2a, nothing is seen, and the second
The image of the identification medium 10 can be seen through the filter 2b. Therefore, even in this case, it is possible to identify the product as a counterfeit product.

[0026]

As described above, according to the present invention, particles of a film having a light-reflecting layer of a polymer cholesteric liquid crystal can be dispersed in ink or the like to print arbitrary characters or designs, and It can cope with diversification. Further, since the film having the light-reflecting layer of the polymer cholesteric liquid crystal can be crushed into particles, the manufacturing is simple and the material cost is reduced, and the manufacturing cost can be significantly reduced. Furthermore, the authenticity of the object can be easily and surely determined by visual observation, and it has an excellent effect that it is difficult to forge.

[Brief description of drawings]

FIG. 1 is a perspective view showing a polymer cholesteric liquid crystal for explaining the principle of the present invention.

FIG. 2 is a perspective view showing circularly polarized light reflected by a polymer cholesteric liquid crystal for explaining the principle of the present invention.

3A is a cross-sectional view showing an object provided with the identification medium of the embodiment, and FIG. 3B is a perspective view showing liquid crystal particles.

FIG. 4 is a perspective view showing an object and a circular polarization filter.

[Explanation of symbols]

1 object 2 circular polarization filter 10 Identification medium 12 Liquid crystal particles

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Claims (3)

[Claims] 1. An object identification medium for optically identifying an object such as a character or a pattern so as to identify the authenticity of the object and reflecting a specific circularly polarized light. An identification medium for an object, wherein the identification display is formed by particles of a film having a light-reflecting layer of a polymer cholesteric liquid crystal having circularly polarized light selectivity. 2. The object identifying medium according to claim 1, wherein the particles of the film are foils, and the surfaces of the particles are arranged substantially parallel to the surface of the object. 3. A method for identifying an object for identifying the authenticity of the object by optically providing an identification mark such as a character or a pattern on the object, and reflecting a specific circularly polarized light. A first filter that forms the above-mentioned identification with particles of a film having a light-reflecting layer of a polymer cholesteric liquid crystal having circularly polarized light selectivity and transmits only circularly polarized light of the light-reflecting layer, and a circle of the light-reflecting layer. A method of identifying an object, characterized in that the object is identified by observing the identification display through a second filter that transmits only circularly polarized light in a direction opposite to the polarized light.